RE: 8b/10b and EMI packaging
JoeL and all:
The coding and EMI is related to certain extent, but EMI is not the main
criteria for code design. The main objective of a code design is a maximum
data rate, and a reliable data recovery, which deal with issues of BER,
base-line wander, clock recovery, minimum transitions per a bit time, and
perhaps some other protocol issues.
After a code meets all these requirements, the frequency spectrum of the
data stream is usually pretty much randomly mixed without a predominant
peaking frequency to cause an specific EMI problem. Very seldom, if any, a
designer has go back to tweak the code to avoid a specific EMI problem,
except the naked twisted pair. The unshielded twisted pair, EMI issue is a
fundamental radiation issue, and it is unfair to blame the coding technique.
I believe we all agree that a coding technique should not add any
unnecessary EMI headache.
Edward S. Chang
NetWorth Technologies, Inc.
[mailto:owner-stds-802-3-hssg@xxxxxxxx]On Behalf Of Joel Goergen
Sent: Thursday, March 16, 2000 7:36 AM
Subject: Re: 8b/10b and EMI packaging
But what you are all missing in your comments is what Tom Truman pointed out
Albuquerque - that the choice of coding is an NRE within an asic, but the
performance, either designed in or designed after the fact, is NOT an NRE
fact, a re-occuring charge each time a product is sold. At what time period
within a project we apply EMI design methods, the size of the project, and
implements those methods, directly relates to the re-occuring costs.
At the last few meetings, everyone had cost as something they want to keep
and about every fourth person presenting indicated 'we all want to make
So, wether we have EMI problems or not, anti-EMI costs money - period. So,
we can stick some of it back into NRE and out of product cost, we all make
The last point Dan Dove already made and that was based on Jonathan's
"This might have been said about 10 or 100 or 1000. We will see. Rather
than choose a "spikey" code and roll the dice, I would recommend
using careful consideration for the code.. then roll the dice. :)"
Just my thoughts
Edward Chang wrote:
> You are right, no question about it. As long as it is cost-effective, all
> parts including component package, board layout, circuit design, cable
> dressing ... should use the good common practice to avoid the unnecessary
> EMI headache.
> Edward S. Chang
> Comment from a reflector-lurker:
> Regarding EMI design, I should point out that the most
> cost-effective system designs take EMI characteristics
> into the basic board designs to such a degree that EMI
> is reduced at the source as much as possible. This
> not only improves the stability and manufacture of the
> designs, but also allows for cheaper packaging materials
> for the enclosures (which can really affect today's
> competitive edge on appearances and cost - use of
> plastics and the like).
> Just my two-cents worth!
> Best to you,
> Wayne Belshaw
> Amdahl Corporation
Member of Technical Staff
High Speed Communications VLSI Research
Bell Laboratories, Lucent Technologies
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